Azure Functions と OpenAI API を使って Line 返答サービスを作ってみる

private static readonly string _messagingApiUrl = "https://api.line.me/v2/bot/message/reply";
private static readonly string _accessToken = "";
private static readonly string _channelSecret = "";
private static readonly string _apiKey = "";
private static HttpClient _httpClient = new HttpClient();

[FunctionName("LineReply")]
public static async Task<IActionResult> Run(
    [HttpTrigger(AuthorizationLevel.Anonymous, "post", Route = null)] HttpRequest req,
    ILogger log)
{
    string requestBody = await new StreamReader(req.Body).ReadToEndAsync();
    req.Headers.TryGetValue("X-Line-Signature", out var xLineSignature);

    log.LogInformation($"Body : {requestBody}");

    var json = System.Text.Json.JsonSerializer.Deserialize<LineMessageReceiveJson>(requestBody);

    log.LogInformation($"Message: {json.events[0].message.text}");
    if (IsSingature(xLineSignature, requestBody, _channelSecret))
    {
        if (json.events[0].type == "message")
        {
            var api = new OpenAIAPI(_apiKey);
            var chat = api.Chat.CreateConversation();
            var prompt = json.events[0].message.text;
            chat.AppendUserInput(prompt);
            var result = await chat.GetResponseFromChatbotAsync();
            // ChatGPTから返答
            await SendTextReplyAsync(json.events[0].replyToken, result);
            return new OkResult();
        }
    }

    return new BadRequestResult();
}

private static async Task SendTextReplyAsync(string replyToken, string message)
{
    _httpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
    _httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", _accessToken);

    var response = await _httpClient.PostAsJsonAsync<LineTextReplyJson>(_messagingApiUrl, new LineTextReplyJson()
    {
        replyToken = replyToken,
        messages = new List<Message>()
                {
                    new Message(){
                        type = "text",
                        text = message
                    }
                }
    });
    response.EnsureSuccessStatusCode();
}

private static bool IsSingature(string signature, string text, string key)
{
    var textBytes = Encoding.UTF8.GetBytes(text);
    var keyBytes = Encoding.UTF8.GetBytes(key);

    using (HMACSHA256 hmac = new HMACSHA256(keyBytes))
    {
        var hash = hmac.ComputeHash(textBytes, 0, textBytes.Length);
        var hash64 = Convert.ToBase64String(hash);

        return signature == hash64;
    }
}

public class LineMessageReceiveJson
{
    public string destination { get; set; }
    public List<Event> events { get; set; }
}

public class Event
{
    public string replyToken { get; set; }
    public string type { get; set; }
    public object timestamp { get; set; }
    public Source source { get; set; }
    public Message message { get; set; }
}

public class Message
{
    public string id { get; set; }
    public string type { get; set; }
    public string text { get; set; }
}

public class Source
{
    public string type { get; set; }
    public string userId { get; set; }
}

public class LineTextReplyJson
    {
        public string replyToken { get; set; }
        public List<Message> messages { get; set; }
        public bool notificationDisabled { get; set; }
    }